IODP Expedition 313, Hole M0027A - Wireline Standard Data

IODP-MSP drilling and logging contractor: ESO

Hole: M0028A

Expedition: 313

Location: New Jersey (NW Atlantic)

Latitude: 39°33.9427′ N

Longitude: 73°29.8348′ W

Logging date: June 05, June 16-18, 2009

Sea floor depth (driller's): 52.42 m DRF

Sea floor depth (logger's): 52.00 m WRF

Total penetration: 668.66 m DSF

Total core recovered:  385.50 m (80.82 % of cored section)

Oldest sediment recovered: Early Miocene

Lithologies: Clays to gravels

Data

The logging data was recorded by the University of Montpellier (Geosciences Montpellier) who are part of the European Petrophysics Consortium (EPC) in .RD format (read by the log software package WellCAD). Data were processed by the European Petrophysics Consortium (EPC). VSP data was recorded and processedby the University of Alberta who were contracted by EPC.

Logging Runs

The depths given in the table are for the processed data. The raw data may contain extra data within the pipe: this data has been removed from the processed data files. The depths in bold refer to top and bottom depths of files before merging (i.e. the top and bottom depth of the final merged files are not in bold).

A complete list of tool and log acronyms is available at http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-acronyms.html.

Logging Nomenclature

The logged intervals in each borehole are described as lower, middle and upper. These do not match across boreholes either in terms of depth or sequence boundary. In any case, logging has not been carried out in more than three stages. These intervals can be seen at

http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-ops-summary.pdf.

General Information

The suite of tools available for logging on Expedition 313 consisted of spectral gamma ray (ASGR), velocity (2PSA), conductivity (DIL45), acoustic borehole imaging (ABI40) and magnetic susceptibility (EM51) measurements. s. Each tool was run separately. Upon coring completion, the spectral gamma log was acquired through drill pipe. Subsequently the hole was conditioned with drill mud. The unfavorable borehole conditions required logging openhole in separate intervals. Difficulties pulling pipe and the development of bridges affected the ability to log certain sections of the boreholes (especially the upper, more unconsolidated sandy sections). The logger’s zero depth position was taken as the top of the drill pipe. Discrepancies in depths between initial zeroing and zeroing on removal of the tool were generally less than 0.5 m. The depths in the table are for the processed logs (after depth shift to the sea floor). Generally, small discrepancies exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from the 'bottom felt' depth in soft sediment. For New Jersey, logging was done from a platform and so there was no ship heave to account for.

Hole M0028A logging

Through-pipe gamma ray measurements were acquired over the entire borehole in two stages. VSP measurements were also acquired over the entire borehole through pipe and in open hole in the lower and middle sections. As in the two other boreholes, drilling began using PQ sized pipe, which was subsequently changed to the smaller diameter HQ pipe at ~400 m. This meant that logs in the lower interval had to fit through a smaller diameter pipe; for this reason, the 2PSA sonic tool was not used, the centralisers being too large to fit through the HQ pipe. Open hole logging operations took place in three stages:

Lower section (425 to 669 m WSF): in this section, borehole conditions were good and the conductivity, magnetic susceptibility and acoustic image tools were run. Only 10 m at the base of the hole could not be logged due to infilling. The conductivity tool was blocked by a bridge that formed at 348.6 m WSF. The two subsequent tools managed to pass this bridge. The acoustic imaging tool was run without centralisers as these exceeded the diameter of the HQ bit.

Middle section (396 to 430 m WSF): this section was expected to be unstable and sandy and to collapse once the HQ pipe was pulled. However, when the VSP tool reached the base of the PQ pipe at the start of VSP acquisition the tool managed to go below the base of the pipe. Subsequently both conductivity and acoustic logs were able to be run for an additional ~20 m of previously unlogged borehole. A large overlap in the conductivity log enabled precise merging of the logs in the middle and lower sections.

Upper section (above 396 m WSF): logging was planned in this section but could not be carried out because the PQ pipe was stuck.

Processing

Depth shift: The original logs were first corrected for the difference in zero tool depths and the difference between logger’s and driller’s zero points (if applicable). For hole M0028A the logger’s zero point was located beneath the driller’s zero in order to make the tool entry and exit point easier to access. See http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-depth-layout.pdf . Finally, logs were depth shifted to the sea floor using the driller’s depth to seafloor (-52.42 m below rig floor). The driller’s distance to seafloor was chosen as the reference depth because for each hole this fell within the range of the depth to seafloor given by the gamma ray log. The gamma ray log through pipe was taken as the reference log (continuous) and where appropriate other logs were depth-matched to it. For M0028A the magnetic susceptibility log required a small linear shift down (0.33 m) to match the spectral gamma log. The log depths are therefore m WMSF.

Data merges: Where there was an overlap the data was merged. Due to the usually excellent match in the overlap section, the data in the merged section was averaged. In hole M0028A the following logs were merged:

DIL45 middle section (run 9) / lower section (run 4)

ASGR through pipe (run 1) / lower section (run 3).

The acquisition of acoustic borehole images occurred in several files due to their size (see image notes for more details).

Environmental corrections: None.

Acoustic data: No acoustic tool was run in this hole.

Spectral gamma ray: Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.

Quality Control

The quality of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of the same tool or down and up logged intervals, and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the acoustic log). 

The quality of the ASGR Spectral Natural Gamma data is directly related to lithology in combination with logging speed. Where counts are lower the reliability of the statistical function used to separate raw counts into values of naturally occurring radioactive elements [potassium (K), uranium (U) and thorium (Th)] is degraded. Negative values are indicative of incorrect statistics; when this is the case, K, U and Th values at that depth has been replaced by a Null (-999.25). Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.

A wide and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall. Hole diameter was calculated from the acoustic imageing tool (ABI40).

Whenever possible, data was acquired downlog, uplog and through the pipe. In this case the uplog is usually the final output. The data recorded within the pipe are usually removed from the final log. This data has been retained in the original data files.

A Null value of -999.25 may replace invalid log values.

Additional information about the drilling and logging operations can be found in the Operations section of the Site Chapter in IODP Proceedings of Expedition 313.
For further questions about the data, please contact:

Jennifer Inwood

University of Leicester

Phone: 011-44-116-252-3327

Fax: 011-44--116-252-3918

E-mail: iodp@le.ac.uk

Johanna Lofi

University of Montpellier 2

Phone: 033- 467-149- 309

Fax: 033- 467- 143- 244

E-mail: iodp@le.ac.uk